Binder for foundry compositions



Patented Apr. 24, 1951 BINDER FOR FOUNDRY COMPOSITIONS Wilbur Euciid Koonce, Laurel, Miss., assignor to Masonite Corporation, Laurel, Miss., a corporation of Delaware No Drawing. Application November 24, 1947, Serial No. 787,847

7 Claims. (Cl. 22-488) This invention relates to a binder for finely divided inorganic materials, the method of making substantially Water-insoluble products by binding finely divided inorganic materials with I proved binder for finely divided inorganic materials. A further object is to provide a method of making substantially water-insoluble molded products consisting essentially of finely divided inorganic materials and a binder therefor in which method said binder is converted into a substantially Water-insoluble state. A more particular object is to provide a binder for foundry sand cores and a method of making said cores employing said binder.

The above objects are accomplished according to this invention by mixing finely divided inorganic material with a binder therefor and water, subjecting the resulting mixture to pressure in a mold having substantially the size and shape of the desired finished article to form a shaped body thereof, heating the shaped body at a temperature and for a period of time sufficient to convert said binder into a strong binder substantially insoluble in water. This binder consists essentially of the water-soluble reaction product resulting from hydrolyzing lignocellulose materials at an elevated temperature and pressure in the presence of moisture.

While the major portion of the description of this invention will be directed to foundry sand cores, because the invention is especially Well suited for this purpose and from all indications this is the field in which it will find a large ap-- plication, nevertheless it is applicable broadly to binding finely divided inorganic materials. Other applications within this broader category will be brought out after the description of the specific embodiment of the invention relative to foundry sand cores.

Heretofore in making foundry sand cores for use in the production of castings, numerous binders have been employed for bonding the sand together. Such binders include oils, cereals, rosins, resins, sulphite waste liquor, proteins, clays, cements, silicates and mixtures thereof. Usually the binder is chosen on the basis of its ability to I render outstanding some especially desired propare all limited in that they are deficient in one .or more of the characteristics listedhereinafter.

As a result, the use of these binders generally involves a compromise wherein at least one of the said listed characteristics is totally or in large part sacrificed in order to achieve the remaining characteristics. g

The characteristics which should be possessed by a binder in order to produce a satisfactory foundry core of wide application are:

l. A binder should impart very low water solubility to the baked core.

2. A binder should possess good dispersing properties so that it can be readily distributed uniformly throughout the core mixture.

3.A binder should produce a mixture which can be formed'into a core without fouling the core boxes or sticking in them.

4. A binder should confer sufficient green strenth on the core so that it will retain its proper form in the green state.

5. A binder should be such that it will not cause distortion of the core during baking.

6. A binder should confer sufficient dry strength on a core so that in the baked core the sand is held together so tenaciously that in the casting operation the flow of molten metal will not wash grains of sand from the surface of the core, and so that the core maintains its proper shape and size until the metal begins to contract and yet so that when the metal starts contracting the core strength decreases accordingly and the core collapses thereby avoiding strains, cracks or hot tears in the casting, and permitting easy removal of the core from the casting.

'7. A binder should generate a minimum of gas during the baking and casting operations.

8. Gas generated, if any, should be harmless to personnel. V

9. A binder should impart sufiicient permeability to a core to allow the escape therethrough of any gases-which may be formed during the baking and casting operations.

10. A binder should be economical to use.

The binder of the instant invention possesses the above properties to a far greater degree than do conventional core binders.

For the sake of clarity and completeness a source of the raw material from which the binder of the present invention is produced will be described.

It is known that lignocellulose materials (hereinafter used synonymously with wood or woody substances for the sake of convenience), e. g. wood of trees and Woody materials of corn stalks and cane and other vegetable growths, can be fibrated further processed for the manufacture of boards or sheet products and the like. One 'of such methods comprises charging a closed chamber or gun (e. g. as set forth in U. S. Patent No. 1,824,221 granted to William H. Mason, September 22, 1931) with relatively small Wood chips,

subjecting the chips to a pressure of about 200 1200 pounds per square inch and a temperature of about 190 C.-300 C. for approximately 30 minutes to 5 seconds, respectively, in the presence of steam, water or other moisture-supplying fluid material, and then discharging the woody material from the gun through a constricted discharge opening therein, e. g. a valve, into a zone of lower pressure (preferably atmospheric pressure) While maintaining substantially the relatively high pressure in the gun, thereby exploding the wood into comparatively finely divided fibers. The above gun conditions depend upon the type of wood, size of the chips (desirably up to 1" long), the water content of the chips (preferably about 25% or more), and other apparent variables. Under this treatment the wood undergoes hydrolysis and the water-insoluble and readily-hydrolyzable constituents are rendered soluble or dispersible or suspendible in Water.

In the board-making industry it has been found necessary to remove from the fiber the greater portion of these water solubles in order to obtain a water-resistant and good board. Such separation may be accomplished by squeezing the fiber with rolls and/0r opposed screws and the like apparatus or more preferably by washing the fiber in water. Thus, briefly, the fiber is passed into a tank and slurried with water and then delivered to and processed by a washer (desirably a countercurrent washer) thereby extracting a quantity of the water solubles such that the used wash water contains roughly 8% of water solubles and such that the fiber, which is further processed and made into boards, contains about 3%-5% (bone dry basis) of water solubles.

This water-soluble material is the starting material from which the water-insoluble binder of the present invention is prepared.

Heretofore the general practice has been to run to waste the wash water laden with the water solubles, with resulting stream pollution, production of noxious odors, and the like evils. The seriousness of this problem is more apparent when considered in view of the fact that a tremendous volume of wash water containin an extremely large quantity (dry basis) of water solubles is involved in a single plant each day.

The hemicellulose fraction of wood, being made up of high molecular weight hexosans and pentosans and comprising some 20% of the original woody tissue, in large part gives rise to the water solubles and is believed to undergo the greatest change during the thermohydrolytic process de' scribed above. It is believed this hydrolysis affects a moderate reduction in molecular weight of the hexosan and pentosan units in producing hexosan and pentosan units soluble in water. These units plus a small amount of lignin, which is similarly rendered soluble in water by the hydrolysis, non-sugar carbohydrates and gums make up the bulk of the water-soluble components. Thus, these water solubles may be appropriately designated hemicellulose extract.

While the hemicellulose extract resulting from the high temperature and pressure hydrolysis of lignocellulose materials as a class is applicable to this invention, the woody material of trees, e. g., pine, gum and the like is preferred. A typical analysis of a hemicellulose xtract according to a preferred embodiment of the instant invention is given in the following table. Pine was used as the source of lignocellulose material.

TABLE I Hemz'cellulose extract composition (bone dry basis) Component: Parts by Weight Hexosans 40 Pentosans 30 Non-sugar carbohydrates l0 Lignin l5 Gums 5 Ash content About 1.5% by wt.

The composition of the hemicellulose extract will vary somewhat depending upon the type of lignocellulose material employed and the particular conditions, e. g., the time, temperature, pressure, etc., under which the lignocellulose material is hydrolyzed. Thus the hemicellulose extract composition can vary approximately as shown in the following table:

TABLE II Hemicellalose extract composition (bone dry basis) Component: Parts by weight Pentosans and hexosans 60-80 Lignin 5-25 Non-sugar carbohydrates 5-15 Gums 2-8 Ash content About 1.5% by wt.

In practicing the instant invention according to a preferred embodiment thereof the hemicellulose extract recovered from the countercurrent washer comprising approximately 8% solids by weight is either evaporated to a more concentrated liquid or spray dried to a powder. Concentrating in conventional triple-effect evaporators to about 50% solids content has been found very satisfactory in producing a concentrate well adapted for the purposes of this invention. Alternatively, if desirable from the standpoint of shipping costs, etc., the 8% concentrate may be spray dried to a powder and then diluted to the desired concentration by redissolving in water just prior to use. In this event the powder should contain not more than about 3% and preferably not more than around 2% moisture until ready for use. It has been found that if the moisture content of the powder exceeds approximately 3%, it tends to cake if not used within a reasonable time after production. Then cores are made using this binder as shown in the example.

The following example illustrates a specific embodiment of this invention. The example compares foundry sand cores, in which the binder of the present invention was used (mixture N0. 1, hemicellulose extract evaporated to 50% concentrate), with cores in which three widely commercial binders were mixed (mixtures No. 2, 3 and 4) Example Four different type mixtures were prepared, the mixtures differing only in the particular type binder employed. In each mixture sand was mixed with, by weight thereof, 4.16% binder (dry basis) and 2.91% water in addition to the water contained in the 50% concentrated binder. Green cores made from each mixture were divid- 5 ed into two lots. One lot was baked 30 minutes and the other lot 60 minutes. All cores were baked at 400 F. The cores were evaluated as shown in the following tabulation:

[Test data given below was obtained by Standard Procedures as outlined in the book on Modern Core Practices and Theories by Harry W. Dietertpublished by Foundrymens Association] Mixture N 1 3 4 Physical Properties Green Cores:

Mold Hardness Permeability"... Compression, p. s. i Deformation, in/in Baked Cores:

60 Min. bake. Tensile strength after subjecting to 100% humidity for 24 hrs. following- 30 Min. bake 0 60 Min. bake Hardness after subjecting to 100% humidity for 24 hrs. following- 30 Min. bake 60 Min. bake. 0 Permeability Retained Strength, p. s. i.:

Cores placed in Dilatomstar 12 Min. 600 F.

after 30 Min. bake L. 60 Min. bake Cores placed in Dilatometer 12 Min. 800 F.

after 60 Min. bake 0 Hot Strength (time, sec., reqd. to collapse 1% x 2" specimens):

Cores placed in Dilatom-' eter 1500? F. under 50# load after- 30 Min. bake 60 Min. bake E. L. means exceeded the 810 p. s. i. limit of testing accessory.

Although about 4%5% binder (dry basis by weight of sand) is preferred, good results are obtained Whenever the binder exceeds about 2%. While good cores can be made using 2% or even less binder, such cores have relatively weak physical properties in the green state and difficulty is likely to be encountered in handling them. The improvement in physical properties obtained with quantities of binder in excess of about 5% normally does not warrant the use of the additional binder. For example. it has been found that somewhat better cores can be made with binder than with 5% binder but the improvement is insuflicient to warrant the use of the greater amount of binder.

The total amount of water which may be used in preparing the green mixtures is dependent upon variables well known to those skilled in the foundry core art. For instance, it is dependent upon the particular size and type casting. Further, it is desirable to adjust the water Applicable baking conditions are sufficiently flexible to be adapted to known foundry practices. Therefore the preferred baking conditions will vary according to the practice of the foundry in which the invention is used. Good cores have been made by baking -5 hours at 475 F.325 F. respectively. For example, the water-soluble binder in the green cores has been converted to a substantially water-insoluble binder resulting in good foundry cores by baking the green cores A hour at 475 F., 4 hour at 425 F., A; hour at 400 F., 1 hour at 375 F. and 5 hours at 325 F. These are the minimum periods of time recommended for baking the cores at the respective temperatures given. ()bviously at any of the given temperatures the baking time can be increased. For instance good cores have been made by baking at a temperature of 400 F. for 2 hours. Temperatures below 325 F. can be used provided correspondingly longer periods of time are used. For example, at a temperature of 300 F. about 20 hours is required. However, by continuing to reduce the temperature a point is reached at which the binder fails to change from the water-soluble to the water-insoluble state, or at least fails to do so within a practical period of time. Thus when a green core was baked at a temperature of 275 F. the binder therein remained substantially water-soluble even after baking 24 hours. The baking can be done at temperatures above 425 F. up to the temperature at which the binder decomposes, however, above'about 425 F. there is practically no reduction in the time required to bake by virtue of the increased temperature.

Still further, as additional applications of the invention in molding finely divided inorganic materials in general, good results were obtained in molding Zinc (metallic powder), graphite, coal dust, and emery dust. In making these mixtures, 5% binder, based on the weight of the inorganic material, in powder form Was milled 5 minutes in a Baker-Perkins mixer. With addition of Water, milling Was continued for 5 minutes and a uniform mixture Was obtained, the amount of water used being based on that required to produce a uniform mixture with ease. Specimens (1% diameter x 1" long) from each of these mixtures were made in a preform mold under 100 p. s. 1. pressure. These specimens were baked and then tested for compressive strength and water resistance. Compressive strength was made with a Universal Testing machine. Water resistance was determined by submerging the specimen in water for 24 hours and thendetermining solubility or softening. All specimens were substantially insoluble in Water and maintained their hardness. The following tabulation summarizes the most pertinent preparation and content to a practical working range and such test data.

Per Baked Com- Finely Divided Inorganic Cent aj fi g a 3 32" pressive Material Water a 0 er Strength,

. IS. 1. SH merslon p s.

Zinc (metallic powder). 2. 4 375 2 Insoluble 13, 500 Graphite 8. 6 375 2 do 585 Coal Dust (Bituminous) 13.3 338 2 13, 330 Emery Dust 6. 2 375 2 2, 260

that the mixtures will work clean in the corel 'tt l box.

The baking conditions may be varied over a It is to be understood that the above examples are for the purpose of illustration only and that the invention broadly comprises molded products wide range within the purview of this invention. consisting essentially of finely divided inorganic material held together by a binder and a method of preparing said products including mixing finely divided inorganic material with a binder therefor and water, subjecting the resulting mixture to pressure in a mold having substantially the size and shape of the desired finished product to form a shaped body thereof, heating the shaped body at a temperature and for a period of time sufficient to convert said binder into a strong binder substantially insoluble in water, said binder consisting essentially of the watersoluble reaction product resulting from hydrolyzing lignocellulose materials at an elevated temperature and pressure in the presence of moisture.

As many apparently widely different embodimerits of this invention may be made without departing from the spirit and scope thereof, it

is to be understood that the invention is not to be limited to the specific embodiments thereof except as defined in the appended claims.

I claim:

1. Method of making molded products comprising mixing finely divided inorganic material with a binder therefor and water, subjecting said mixture to pressure in a mold having the size and shape of the desired finished product to form a shaped body thereof, heating said shaped body at a temperature and for a period of time sufficient to convert said binder into a strong binder substantially insoluble in water, said binder consisting essentially of the water-soluble reaction product resulting from hydrolyzing lignocellulose material at an elevated temperature and pressure in the presence of moisture, and comprising, weight thereof, the following components in about the proportions given:

Components: Parts by weight Pentosans and hexosans 60-80 Lignin -25 Non-sugar carbohydrates 5-15 Gums 2-8 2, Method of making foundry sand cores comprising mixing sand With a binder therefor and water, subjecting said mixture to pressure in a mold having the size and shape of the desired finished product to form a shaped body thereof, heating said shaped body at a temperature and for a period of time sufficient to convert said binder into a strong binder substantially insoluble in water, said binder consisting essentially of the water-soluble reaction product resulting from hydrolyzing lignocellulose material at an elevated temperature and pressure in the presence of moisture, and comprising, by weight thereof, the following components in about the proportions given:

Components: Parts by weight Pentosans and hexosans 60-30 Lignin 5-25 Non-sugar carbohydrates 5-15 Gums 2-8 8 vated' temperature and pressure in the presence of moisture, and comprising, by Weight thereof, the following components in about the proportions given:

Components: Parts by weight Pentosans and hexosans 70 Lignin 15 Non-sugar carbohydrates 10 Gums 5 4. Molded products comprising finely divided inorganic material and a substantially waterinsoluble binder thereof; said binder consisting essentially of the heat reaction product of the following components in about the proportions given:

Components: Parts by weight Pentosans and hexosans 60-80 Lignin 5-25 Non-sugar carbohydrates 5-15 Gums 2-8 5. Molded products comprising finely divided inorganic material and a substantially waterinsoluble binder therefor; said binder consisting essentially of the heat reaction product of the following components in about the proportions given:

Components: Parts by weight Pentosans and hexosans 70 Lignin Non-sugar carbohydrates 10 Gums 5 6. Baked foundry cores comprising sand and a substantially water-insoluble binder therefor; said binder consisting essentially of the heat reaction product of the following components in about the proportions given:

Components: Parts by weight Pentosans and hexosans -80 Lignin 5-25 Non-sugar carbohydrates 5-15 Gums 2-8 7. Baked foundry cores comprising sand and a substantially water-insoluble binder therefor, sadi binder consisting essentially of the heat reaction product of the following components in about the proportions given:

Components: Parts by weight Pentosans and hexosans Lignin 15 Non-sugar carbohydrates 10 Gums 5 WILBUR EUCLID KOO'NCE.

REFERENCES CEEED The following references are of record in the rile of this patent:

UNITED STATES PATENTS Number 

4. MOLDED PRODUCTS COMPRISING FINELY DIVIDED INORGANIC MATERIAL AND A SUBSTANTIALLY WATERINSOLUBLE BINDER THEREOF: SAID BINDER CONSISTING ESSENTIALLY OF THE HEAT REACTION PRODUCT OF THE FOLLOWING COMPONENTS IN ABOUT THE PROPORTIONS GIVEN. 